Can it be connected to a wire which is controlled by an external switch (normal switch on the wall)?That means that the external switch will cut the power to the lamp.Will on imidiatly when the power is turned on? Then we can use the remote (and app) as a dimmer and control color.

The reason is that the wires in the roof where we want the lamp is already controlled by a switch, and that switch also controls 2 other lamps, so we cannot have it constant ON, but it its ok as long as the Yeelight goes on and of with the switch like a normal lamp.